how do I clear a list?

Hello!
This is my very first attempt to produce some script.

I would like to create a vb component, that, for now, reads a list of integers, and produces a list of the same integers, but deleting from that every number already occurred.

But I ran into some problems

Here is the screenshot of the first attempt:and here the script:

Dim voxel_out As New list (Of Integer)
Dim voxel_in As New list (Of Integer)
Dim voxel_in_service As New list (Of Integer)
Dim a As Integer
Dim i As Integer
Dim x As Integer
voxel_in = VoxelListIN
For x = 0 To voxel_in.count() - 1
a = voxel_in(0)
voxel_out.add(a)
'deletes form voxel_in all the repetitions of a:
For i = 1 To voxel_in.count() - 1
If voxel_in(i) <> a Then
voxel_in_service.add(voxel_in(i))
End If
Next
voxel_in = voxel_in_service
voxel_in_service.clear()
Next
VoxelListOut = Voxel_out

the problem with this script is that it says, as an error, that "the index is not included in the interval. It is requested a value which is not negative and smaller than the dimension of the set". The same kind of error I get when I screw up with the indices of the FOR command.
The strange thing is that if I remove the

voxel_in_service.clear()

line, the script runs without errors (but of course, with a wrong result).

Therefore I thought it was because the .clear method was not fully supported, so I wrote the following:

Dim voxel_out As New list (Of Integer)
Dim voxel_in As New list (Of Integer)
Dim voxel_in_service As New list (Of Integer)
Dim reset_list As New List (Of Integer)
Dim a As Integer
Dim i As Integer
Dim x As Integer
voxel_in = VoxelListIN
For x = 0 To voxel_in.count() - 1
a = voxel_in(0)
voxel_out.add(a)
'deletes form voxel_in all the repetitions of a:
For i = 1 To voxel_in.count() - 1
If voxel_in(i) <> a Then
voxel_in_service.add(voxel_in(i))
End If
Next
voxel_in = voxel_in_service
voxel_in_service = reset_list
Next
VoxelListOut = Voxel_out
reset = reset_list

but, very surprisingly to me, the line

voxel_in_service = reset_list

instead of setting back voxel_in_service to it's original state, sets, as you can see from the "reset" output, reset_list to the values of Voxel_in_service. Why is it doing that?!
Thank you very much!

Replies to This Discussion

Permalink Reply by Michael Pryor on October 24, 2013 at 11:22am

The set component does this.

Permalink Reply by Matteo Falduto on October 24, 2013 at 11:30am

I know there are some simpler ways to do that, but I decided to script it for learning how to script and also because this is just a part of what I want to achieve with the final script...

but thank you anyway for your reply!

Permalink Reply by Thomas on October 24, 2013 at 4:36pm

Hi Matteo,
First get clear about the difference between value types (e.g. Integer) and reference types (e.g. List).

You have written:

voxel_in = voxel_in_service
voxel_in_service.clear()

After the first line both voxel_in and voxel_in_services are referring to the same list. If you clear the list stored in voxel_in_service then you also clear the list stored in voxel_in because it is the same. Both variables are now referring to an empty list!

You have to do something like that:

voxel_in.Clear()
voxel_in.AddRange(voxel_in_service)
voxel_in_service.Clear()

The next problem is that your For loop gets from 0 to voxel_in.count() - 1. But the length of voxel_in is changing! Use a While loop instead:

While (voxel_in.Count > 0)
...
End While

After these changes your code should work.

A shorter way to remove duplicates:

If (list.Count = 0) Then Return

list.Sort()

Dim i = 1

While (i < list.Count)
If (list(i - 1) = list(i)) Then
list.RemoveAt(i)
End If
i += 1
End While

Or use the build-in method:

list = list.Distinct().ToList()